EP0160096A1 - Approaching method in area machining - Google Patents

Approaching method in area machining Download PDF

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Publication number
EP0160096A1
EP0160096A1 EP84903761A EP84903761A EP0160096A1 EP 0160096 A1 EP0160096 A1 EP 0160096A1 EP 84903761 A EP84903761 A EP 84903761A EP 84903761 A EP84903761 A EP 84903761A EP 0160096 A1 EP0160096 A1 EP 0160096A1
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EP
European Patent Office
Prior art keywords
cutting
starting point
approach
area
tool
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EP84903761A
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German (de)
French (fr)
Inventor
Hajimu Kishi
Masaki Seki
Takashi Takegahara
Yasushi Onishi
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Fanuc Corp
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Fanuc Corp
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
    • G05B19/182—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by the machine tool function, e.g. thread cutting, cam making, tool direction control
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/49—Nc machine tool, till multiple
    • G05B2219/49381—Raster, line servo, area machining, cutting, facing
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/50—Machine tool, machine tool null till machine tool work handling
    • G05B2219/50109—Soft approach, engage, retract, escape, withdraw path for tool to workpiece
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T408/00—Cutting by use of rotating axially moving tool
    • Y10T408/16—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor
    • Y10T408/17—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor to control infeed
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T408/00—Cutting by use of rotating axially moving tool
    • Y10T408/16—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor
    • Y10T408/175—Cutting by use of rotating axially moving tool with control means energized in response to activator stimulated by condition sensor to control relative positioning of Tool and work
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T409/00—Gear cutting, milling, or planing
    • Y10T409/30—Milling
    • Y10T409/30084—Milling with regulation of operation by templet, card, or other replaceable information supply
    • Y10T409/300896—Milling with regulation of operation by templet, card, or other replaceable information supply with sensing of numerical information and regulation without mechanical connection between sensing means and regulated means [i.e., numerical control]

Definitions

  • This invention relates to a method of approach in area cutting for cutting the interior of an area surrounded by the curve of an external shape. More particularly, the invention relates to a method of approach so adapted that in moving a tool toward a cutting starting point, the tool is moved obliquely with respect to a workpiece so that the tool will cut into the workpiece without fail.
  • Forms of numerically controlled machining include cutting in which the interior of an area bounded by the curve of an external shape is hollowed out down to a predetermined depth, and die milling in which the interior of an area is die milled.
  • an end mill includes a bottom surface having cutting edges BT1, BT2, and a cutter side having a cutting edge BT3. Longitudinal cutting is performed by the cutting edges BT1, BT2, and transverse cutting is carried out by the cutting edge BT3. Little cutting force is applied in the longitudinal direction, and great cutting force in the transverse direction.
  • the workpiece is a solid material prior to the cutting of an area.
  • the center position CP (see Fig. 2) of the bottom surface of tool (end mill) TL does not rotate (i.e., is stationary) even when the tool TL is rotated. Consequently, when the initial cut is to be made, even though the tool TL is moved for cutting feed from an approach starting point P a , which is located directly above the cutting starting point P i shown in Fig. 3, toward the cutting starting point P i while being rotated, the tool TL slides along the surface of the workpiece WK rather than cutting into the workpiece or, even if it does cut into the workpiece, it fails to do so smoothly and results in a machining error.
  • An object of the present invention is to provide a method of approach in area cutting whereby a tool will cut into a workpiece without fail when making an approach even at initial cutting.
  • Another object of the present invention is to provide a method of approach in area cutting whereby a tool will cut into a workpiece without fail when making an approach even if a hole or the like is not bored beforehand at the cutting starting point.
  • the present invention provides a method of approach in area cutting for cutting the interior of an area bounded by the curve of an external shape.
  • the method includes giving in advance an angle 0 between a workpiece plane and a straight line connecting an approach starting point and a cutting starting point, and a distance dz between the approach starting point and the cutting starting point in a direction perpendicular to the workpiece plane, calculating coordinate values of the approach starting point using the angle 9 and the distance dz in such a manner that a projection of the straight line on the workpiece plane is brought into coincidence with a direction of a normal line at the cutting starting point on the curve of the external shape, positioning the tool at the approach starting point in a rapid-traverse mode, subsequently moving the tool to the cutting starting point in a cutting-feed mode, and thereafter starting cutting.
  • the tool TL is moved toward the cutting starting point obliquely with respect to the workpiece WK.
  • the tool is capable of cutting into the workpiece smoothly without fail.
  • Fig. 1 is a view for describing the cutting of an area
  • Fig. 2 is a view for describing a tool
  • Fig. 3 is a view for describing the shortcomings of the conventional method
  • Fig. 4 is a view for describing a method of approach in area cutting according to the present invention
  • Fig. 5 is a block diagram of an embodiment of the present invention
  • Fig. 6 is a flowchart of processing according to the present invention.
  • Fig. 4 is a view for describing the present invention, in which (A) is a sectional view and (B) a plan view.
  • the method of approach of the present invention includes giving in advance an angle 6 between a workpiece plane WPL and a straight line SL connecting an approach starting point P A and a cutting starting point P i , and a distance dz between the approach starting point P A and the cutting starting point P i in a direction perpendicular to the workpiece plane, calculating coordinate values of the approach starting point P A using the angle 8 and the distance dz in such a manner that a projection SL' [see Fi g .
  • Fig. 5 is a block diagram of an embodiment of the present invention
  • Fig. 6 is a flowchart of processing.
  • an item of NC data is an M-, S- or T-function instruction
  • the processor delivers the data to a machine tool 107 via a data input/output unit 106 functioning as an interface circuit between an NC unit and the machine.
  • the processor causes the NC data reader 103 to read the next item of NC data. If the item of NC data is path data, then the following path control processing is executed.
  • the processor delivers ⁇ X , ⁇ Y , ⁇ Z to a pulse distributor 108 every ⁇ T sec.
  • the pulse distributor 108 performs a simultaneous three-axis pulse distribution calculation to generate distributed pulses Xp, Yp, Zp.
  • the distributed pulses are applied as inputs to servo circuits 109X, 109Y, 109 Z for the respective axes to rotate servomotors 110X, 110Y, 110Z.
  • the tool is thus moved relative to the workpiece toward a target position.
  • the processor 102 updates the present position X a , Y a Z a along the respective axes every aT sec, X a , Y a , Z a having been stored in a working memory 112:
  • the processor 102 updates remaining traveling distances X , Y r , Z r (the initial values of which are the incremental values X i , Y i , Z i , respectively) every ⁇ T sec, X r , Y , Z r having been stored in the working memory 112:
  • the processor 102 then causes the NC data reader 103 to read the next item of NC data.
  • the processor 102 causes the NC data reader 103 to read the area cutting data and store the data in a RAM 111 until the code indicating the end of the area cutting data is read out.
  • the area cutting data are (1) data indicating the curve of the external shape of the area, (2) cutting direction data (data indicating that the tool is to be moved in the direction of the arrow A or in the direction of an arrow D in Fig. 1), (3) cut-in direction data (data indicating that the tool is to be moved in the direction of the arrow B or in the direction of an arrow C in Fig.
  • the processor 102 performs the operation on i, which is stored in the working memory 112.
  • the cutting direction is the +X direction
  • the cut-in direction is the +Y direction
  • the approach plane is parallel to the XY plane at a height Z a p
  • the cut-in direction starting point is Y s
  • the cut-in direction end point is Y e .
  • the processor 102 performs processing for specifying an i-th cutting path PT i . Specifically, the processor 102 creates the straight line SL i (see Fig. 1). The straight line SL i is expressed by the equation
  • the processor 102 calculates the coordinate values of the points P i , Q i where the straight line SL i intersects the curve OLC of the external shape of the area.
  • the intersection point Pi which has the smaller X coordinate value
  • the intersection point Q i which has the larger X coordinate value
  • the processor 102 calculates the coordinate values (X A' Y A' Z A ) of the approach starting point P A by using the coordinate values of the cutting starting point P i , the angle a and the distance dz. More specifically, first the processor finds the normal line to the external shape curve OLC [see Fig. 4(B)] at the cutting starting point P i .
  • the normal line lies on the XY plane and is obtained in the following manner:
  • the straight line connecting the center of this circle and the cutting starting point P i will be the normal line. Accordingly, the normal line is specified by the equation where a and b are coefficients.
  • X A , Y A be the coordinate values of the approach starting point P a along the X and Y axes, respectively, the following equation will hold: For a case where the curve OLC of the external shape is composed of a number of line segments and circular arcs, if the cutting starting point P i lies on a predetermined line segment, then the normal line will be a straight line perpendicular to the line segment and passing through the cutting starting point; if the cutting starting point P i lies on a predetermined circular arc, then the normal line will be a straight line connecting the cutting starting point P i and the center of the circular arc.
  • the processor 102 obtains the coordinate values (X A , Y A' Z A ) of the approach starting point from Eqs. (7) 1 through (10).
  • the processor 102 moves the tool TL along the Z axis from the present position (not shown) to a point Ps [see Fig. 4(A)] on the approach plane APL in the rapid-traverse mode, thereafter positions the tool at a point P A ' on the approach plane APL in the rapid-traverse mode by simultaneous two-axis control along the X and Y axes, and then moves the tool along the Z axis to the approach starting point P A in the rapid-traverse mode. This completes positioning of the tool TL at the approach starting point P A .
  • the processor 102 obtains incremental quantities X i , Y i , Z i between P A and P i and executes the path control processing of the step (4) by using these incremental quantities and the cutting velocity F.
  • the tool TL is transported from the approach starting point P A to the cutting starting point P i at the cutting velocity F.
  • the tool begins to cut workpiece WK and finally arrives at the cutting starting point P i . This completes the approach operation.
  • the processor 102 treats the point P i as the cutting starting point and the point Q i as the cutting end point and, in like fashion, moves the tool along the +X axis in the rapid-traverse mode to perform cutting along the i-th cutting path.
  • an area cutting command is inserted into the NC tape
  • an approach path and cutting paths are created by using the area cutting data that follow the area cutting command, and area cutting is performed along these paths.
  • an arrangement can be adopted in which NC data for moving the tool along the approach path and cutting paths are created by the aforementioned method, the NC data are recorded on an NC tape, and approach and cutting control are performed by feeding the NC data recorded on the NC tape into an NC unit.
  • a tool is made to approach a workpiece plane obliquely so that the workpiece may be cut by the cutting edge formed at the cutter side.
  • This enables an improvement in cutting performance, allows the tool to cut into the workpiece smoothly when an approach is made, and permits cutting to be performed efficiently.
  • a hole or the like need not be bored in advance at the cutting starting point. This shortens machining time and enables highly accurate area cutting to be performed. Accordingly, the present invention is well-suited for application to NC data creation systems for machine tool control or area cutting control wherein area cutting is performed by numerical control.

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  • Engineering & Computer Science (AREA)
  • Human Computer Interaction (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Numerical Control (AREA)
  • Milling Processes (AREA)

Abstract

An approaching method in an area machining includes the steps of: previously providing an angle ε made by a work plane (WPL) and a straight line (SL) which connects together an approaching start point (PA) and a cutting start point (Pi) and a distance dz between the approaching start point (PA) and the cutting start point (P,) in the direction perpendicular to the work plane; calculating coordinate values representing the approaching start point (PA) by the use of the angle θ and the distance dz such that a projected straight line (SL') obtained by projecting the straight line (SL) on the work plane (WPL) extends in the normal direction of an outline curve (OLC) at the cutting start point (Pi); positioning a tool (TL) at the approaching start point (PA) at a rapid traverse; moving the tool to the cutting start point (Pi) at a feed rate for cutting; and starting cutting.

Description

    Technical Field
  • This invention relates to a method of approach in area cutting for cutting the interior of an area surrounded by the curve of an external shape.. More particularly, the invention relates to a method of approach so adapted that in moving a tool toward a cutting starting point, the tool is moved obliquely with respect to a workpiece so that the tool will cut into the workpiece without fail.
    • Background Art
  • Forms of numerically controlled machining include cutting in which the interior of an area bounded by the curve of an external shape is hollowed out down to a predetermined depth, and die milling in which the interior of an area is die milled. In such cutting of the interior of an area, as shown in Fig. 1, the process includes entering the curve OLC of an external shape of an area AR, cutting direction (direction of arrow A), cut-in direction (direction of arrow B), and cut-in pitch P, creating a cutting-path PTi (i=l, 2,...) on the basis of the entered data, performing cutting by moving a tool TL in the cutting direction along the created cutting path PT., creating the next cutting path PTi+1 by effecting a shift corresponding to the aforementioned pitch in the cut-in direction (direction of arrow B) after the completion of cutting along the abovementioned cutting path, performing cutting by moving the tool in the cutting direction (direction of arrow A) along the next cutting path, and thereafter repeating this unidirectional cutting to cut the area AR. It should be noted that, for each cutting path PTi, two points Pi, Q1 where the curve OLC of the external shape is intersected by a straight line SLi decided by the cut-in direction and pitch are specified as machining starting and end points, respectively. A tool referred to as an end mill is used as the tool TL. As shown in Fig. 2, an end mill includes a bottom surface having cutting edges BT1, BT2, and a cutter side having a cutting edge BT3. Longitudinal cutting is performed by the cutting edges BT1, BT2, and transverse cutting is carried out by the cutting edge BT3. Little cutting force is applied in the longitudinal direction, and great cutting force in the transverse direction.
  • The workpiece is a solid material prior to the cutting of an area. Moreover, the center position CP (see Fig. 2) of the bottom surface of tool (end mill) TL does not rotate (i.e., is stationary) even when the tool TL is rotated. Consequently, when the initial cut is to be made, even though the tool TL is moved for cutting feed from an approach starting point Pa, which is located directly above the cutting starting point Pi shown in Fig. 3, toward the cutting starting point Pi while being rotated, the tool TL slides along the surface of the workpiece WK rather than cutting into the workpiece or, even if it does cut into the workpiece, it fails to do so smoothly and results in a machining error.
  • Accordingly, a hole is bored in advance at the initial cutting starting point Pi so that the tool TL will be sure to cut into the workpiece WK when the approach is made. However, this method is disadvantageous in that it necessitates the hole boring step prior to the cutting of the area and prolongs machining time.
  • An object of the present invention is to provide a method of approach in area cutting whereby a tool will cut into a workpiece without fail when making an approach even at initial cutting.
  • Another object of the present invention is to provide a method of approach in area cutting whereby a tool will cut into a workpiece without fail when making an approach even if a hole or the like is not bored beforehand at the cutting starting point.
    • Disclosure of the Invention
  • The present invention provides a method of approach in area cutting for cutting the interior of an area bounded by the curve of an external shape. The method includes giving in advance an angle 0 between a workpiece plane and a straight line connecting an approach starting point and a cutting starting point, and a distance dz between the approach starting point and the cutting starting point in a direction perpendicular to the workpiece plane, calculating coordinate values of the approach starting point using the angle 9 and the distance dz in such a manner that a projection of the straight line on the workpiece plane is brought into coincidence with a direction of a normal line at the cutting starting point on the curve of the external shape, positioning the tool at the approach starting point in a rapid-traverse mode, subsequently moving the tool to the cutting starting point in a cutting-feed mode, and thereafter starting cutting. According to the approach method of the present invention, the tool TL is moved toward the cutting starting point obliquely with respect to the workpiece WK. As a result, even though the workpiece is a solid member when the approach is made, the tool is capable of cutting into the workpiece smoothly without fail.
    • Brief Description of the Drawings
  • Fig. 1 is a view for describing the cutting of an area, Fig. 2 is a view for describing a tool, Fig. 3 is a view for describing the shortcomings of the conventional method, Fig. 4 is a view for describing a method of approach in area cutting according to the present invention, Fig. 5 is a block diagram of an embodiment of the present invention, and Fig. 6 is a flowchart of processing according to the present invention.
    • Best Mode for Carrying Out the Invention
  • Fig. 4 is a view for describing the present invention, in which (A) is a sectional view and (B) a plan view. The method of approach of the present invention includes giving in advance an angle 6 between a workpiece plane WPL and a straight line SL connecting an approach starting point PA and a cutting starting point Pi, and a distance dz between the approach starting point PA and the cutting starting point Pi in a direction perpendicular to the workpiece plane, calculating coordinate values of the approach starting point PA using the angle 8 and the distance dz in such a manner that a projection SL' [see Fig. 4(B)] of the straight line SL on the workpiece plane WPL is brought into coincidence with a direction of a normal line at the cutting starting point Pi on the curve OLC of the external shape, positioning the tool TL at the approach starting point PA in a rapid-traverse mode, subsequently moving the tool to the cutting starting point Pi in a cutting-feed mode, and thereafter starting cutting.
  • Fig. 5 is a block diagram of an embodiment of the present invention, and Fig. 6 is a flowchart of processing.
    • (1) When a cycle start button on an operator's panel 101 is pressed, a processor 102 causes an NC data reader 103 to read one block of NC data from an NC tape 104. The NC tape 104 stores area cutting data in addition to ordinary path data, G-function instruction data and M-, S- and T-function instruction data. Stored at the end of the NC program is an M code (M02) indicating program end. Placed at the beginning of the area cutting data is an area cutting command indicating that the data which follow are the area cutting data. Placed at the end of the area cutting data is a code indicative of the end of the area cutting data.
    • (2) The processor 102, placed under the control of a control program stored in a ROM 105, checks whether an item of the read NC data is "M02", which is indicative of program end. If the item of data is "M02", numerical control processing is ended.
    • (3) If the item of read NC data is not "M02" indicative of program end, then the processor 102 checks whether the item of NC data is the area cutting command.
    • (4) If the item of NC data is not the area cutting command, the processor 102 executes ordinary numerical control processing.
  • By way of example, if an item of NC data is an M-, S- or T-function instruction, the processor delivers the data to a machine tool 107 via a data input/output unit 106 functioning as an interface circuit between an NC unit and the machine. In response to a completion signal received as an answer from the machine tool 107 indicating completion of processing for the M-, S- or T-function instruction, the processor causes the NC data reader 103 to read the next item of NC data. If the item of NC data is path data, then the following path control processing is executed. Specifically, the processor obtains incremental values Xi, Yi, Zi along the respective axes, obtains velocity components Fx, Fv, Fz along the respective axes from equations
    Figure imgb0001
    Figure imgb0002
    Figure imgb0003
    based on the incremental values and a commanded feed velocity F, thereafter obtains travelling quantities ΔX, ΔY, ΔZ, which are to be traversed along the respective axes in a predetermined period of time ΔT seconds (= 8 msec), from equations
    Figure imgb0004
    Figure imgb0005
    Figure imgb0006
  • The processor delivers ΔX, ΔY, ΔZ to a pulse distributor 108 every ΔT sec. On the basis of the input data (aX, ΔY, ΔZ), the pulse distributor 108 performs a simultaneous three-axis pulse distribution calculation to generate distributed pulses Xp, Yp, Zp. The distributed pulses are applied as inputs to servo circuits 109X, 109Y, 109Z for the respective axes to rotate servomotors 110X, 110Y, 110Z. The tool is thus moved relative to the workpiece toward a target position.
  • The processor 102, in accordance with the following formulae, updates the present position Xa, Ya Za along the respective axes every aT sec, Xa, Ya, Za having been stored in a working memory 112:
  • Figure imgb0007
    Figure imgb0008
    Figure imgb0009
    The sign depends upon the direction of movement. Similarly, in accordance with the following formulae, the processor 102 updates remaining traveling distances X , Yr, Zr (the initial values of which are the incremental values Xi, Yi, Zi, respectively) every ΔT sec, Xr, Y , Zr having been stored in the working memory 112:
    Figure imgb0010
    Figure imgb0011
    Figure imgb0012
    When the following condition is established:
    Figure imgb0013
    the processor 102 then causes the NC data reader 103 to read the next item of NC data.
  • (5) If the item of NC data is found to be the area cutting command at the decision step (3), the processor 102 causes the NC data reader 103 to read the area cutting data and store the data in a RAM 111 until the code indicating the end of the area cutting data is read out. It should be noted that the area cutting data are (1) data indicating the curve of the external shape of the area, (2) cutting direction data (data indicating that the tool is to be moved in the direction of the arrow A or in the direction of an arrow D in Fig. 1), (3) cut-in direction data (data indicating that the tool is to be moved in the direction of the arrow B or in the direction of an arrow C in Fig. 1), (4) pitch P in the cut-in direction, (5) cutting velocity, (6) cut-in direction starting point, (7) cut-in direction end point, (8) position (Z ap of approach plane APL [see Fig. 4(A)], (9) the angle θ between the workpiece plane and a straight line connecting the approach starting point PA and cutting starting point Pi, and (10) the distance dz between the approach starting point PA and the cutting starting point Pi in a direction perpendicular to the workpiece plane, etc.
  • (6) When the area cutting data are finished being read, the processor 102 performs the operation
    Figure imgb0014
    on i, which is stored in the working memory 112. Hereafter we will assume that the cutting direction is the +X direction, that the cut-in direction is the +Y direction, that the approach plane is parallel to the XY plane at a height Z ap , that the cut-in direction starting point is Ys, and that the cut-in direction end point is Ye.
  • (7) Next, the processor 102 performs processing for specifying an i-th cutting path PTi. Specifically, the processor 102 creates the straight line SLi (see Fig. 1). The straight line SLi is expressed by the equation
    Figure imgb0015
  • (8) Thereafter, the processor 102 calculates the coordinate values of the points Pi, Qi where the straight line SLi intersects the curve OLC of the external shape of the area. Of the intersection points Pit Qi, the intersection point Pi, which has the smaller X coordinate value, is treated as the cutting starting point of the i-th cutting path PTi, and the intersection point Qi, which has the larger X coordinate value, is treated as the cutting end point of the i-th cutting path PTi.
  • (9) After the coordinate values (Xio, Yio' Zio) of the cutting starting point Pi are calculated in the above manner, the processor 102 calculates the coordinate values (XA' YA' ZA) of the approach starting point PA by using the coordinate values of the cutting starting point Pi, the angle a and the distance dz. More specifically, first the processor finds the normal line to the external shape curve OLC [see Fig. 4(B)] at the cutting starting point Pi. The normal line lies on the XY plane and is obtained in the following manner:
  • If two points Pil, Pi2 lying on the external shape curve OLC on either side of the cutting starting point Pi are found and a circle passing through these three points Pil, Pi, Pi2 is obtained, then the straight line connecting the center of this circle and the cutting starting point Pi will be the normal line. Accordingly, the normal line is specified by the equation
    Figure imgb0016
    where a and b are coefficients. Letting XA, YA be the coordinate values of the approach starting point Pa along the X and Y axes, respectively, the following equation will hold:
    Figure imgb0017
    For a case where the curve OLC of the external shape is composed of a number of line segments and circular arcs, if the cutting starting point Pi lies on a predetermined line segment, then the normal line will be a straight line perpendicular to the line segment and passing through the cutting starting point; if the cutting starting point Pi lies on a predetermined circular arc, then the normal line will be a straight line connecting the cutting starting point Pi and the center of the circular arc.
  • If we assume that the projection of the approach starting point PA (XA, YA, ZA) on a cutting plane CPL is Pi', the three-dimensional coordinate values thereof will be (XA, YA, Zio). Accordingly, letting D be the distance between the cutting starting point Pi and the projected point Pi', the following equations will hold:
    Figure imgb0018
    Figure imgb0019
    Figure imgb0020
  • On the basis of the foregoing the processor 102 obtains the coordinate values (XA, YA' ZA) of the approach starting point from Eqs. (7)1 through (10).
  • (10) When the coordinate values of the approach starting point PA are thus obtained, the processor 102 moves the tool TL along the Z axis from the present position (not shown) to a point Ps [see Fig. 4(A)] on the approach plane APL in the rapid-traverse mode, thereafter positions the tool at a point PA' on the approach plane APL in the rapid-traverse mode by simultaneous two-axis control along the X and Y axes, and then moves the tool along the Z axis to the approach starting point PA in the rapid-traverse mode. This completes positioning of the tool TL at the approach starting point PA. It should be noted that the numerical control processing for the positioning from the present position to the point P , from the point PS to the point PA' and from the point PA' to the point PA is performed in a manner similar to the path control processing of the step (4).
  • (11) When positioning of the tool at the approach starting point PA is concluded, the processor 102 obtains incremental quantities Xi, Yi, Zi between PA and Pi and executes the path control processing of the step (4) by using these incremental quantities and the cutting velocity F. As a result, the tool TL is transported from the approach starting point PA to the cutting starting point Pi at the cutting velocity F. In thA course of travel the tool begins to cut
    Figure imgb0021
    workpiece WK and finally arrives at the cutting starting point Pi. This completes the approach operation.
  • (12) When the approach is completed, the processor 102 treats the point Pi as the cutting starting point and the point Qi as the cutting end point and, in like fashion, moves the tool along the +X axis in the rapid-traverse mode to perform cutting along the i-th cutting path.
  • (13) When cutting is completed, the processor 102 obtains the difference (= |Ye-Ya|) between the present position coordinate Ya (stored in the working memory 112) along the Y axis and Y-axis coordinate Ye of the cut-in direction end point and checks whether or not the difference is greater than the pitch quantity P.
  • (14) If |Ye-Ya| > P holds, the processor 102 performs the operation
    Figure imgb0022
    and repeats the processing from step (7) onward.
  • (15) If |Ye-Ya| < P is found to hold at the decision step (13), then the processor 102 finally performs cutting by transporting the tool along the curve OLC of the external shape of the area, thereafter causes the NC data reader 103 to read the next item of NC data and repeats the processing from step (2) onward.
  • Though the present invention has been described in detail in accordance with the drawings, the invention is not limited to the illustrated embodiment. For example, in the embodiment described an area cutting command is inserted into the NC tape, an approach path and cutting paths are created by using the area cutting data that follow the area cutting command, and area cutting is performed along these paths. However, an arrangement can be adopted in which NC data for moving the tool along the approach path and cutting paths are created by the aforementioned method, the NC data are recorded on an NC tape, and approach and cutting control are performed by feeding the NC data recorded on the NC tape into an NC unit.
    • Industrial Applicability
  • According to the present invention, a tool is made to approach a workpiece plane obliquely so that the workpiece may be cut by the cutting edge formed at the cutter side. This enables an improvement in cutting performance, allows the tool to cut into the workpiece smoothly when an approach is made, and permits cutting to be performed efficiently. Further, since the arrangement is such that the tool approaches the workpiece plane obliquely according to the present invention, a hole or the like need not be bored in advance at the cutting starting point. This shortens machining time and enables highly accurate area cutting to be performed. Accordingly, the present invention is well-suited for application to NC data creation systems for machine tool control or area cutting control wherein area cutting is performed by numerical control.

Claims (4)

1. A method of approach in area cutting for cutting the interior of an area bounded by a curve of an external shape, characterized by a first step of entering an angle θ between a workpiece plane and a straight line connecting an approach starting point and a cutting starting point, and a distance dz between the approach starting point and the cutting starting point in a direction perpendicular to the workpiece plane, a second step of calculating coordinate values of said approach starting point using the angle 0 and the distance dz in such a manner that a projection of said straight line on the workpiece plane is brought into orientation with a direction of a normal line at the cutting starting point on the curve of said external shape, and a third step of positioning the tool at the approach starting point, subsequently moving said tool to the cutting starting point in a cutting-feed mode, and thereafter starting cutting in the interior of the area.
2. A method of approach in area cutting according to claim 1, characterized in that, in said second step, the normal line is specified by y = a·x + b, and three-dimensional coordinate values (XA, YA, ZA) of an approach starting point are obtained according to
Figure imgb0023
Figure imgb0024
Figure imgb0025
Figure imgb0026
where Pi' is a projection of an approach starting point PA (XA, YA, ZA) on a plane containing a cutting starting point P. (Xio, Yio, Zio), and D is a distance between Pi and Pi'.
3. A method of approach in area.cutting for cutting the interior of an area bounded by a curve of an external shape, characterized by a first step of entering an angle θ between a workpiece plane and a straight line connecting an approach starting point and a cutting starting point, and a distance dz between the approach starting point and the cutting starting point in a direction perpendicular to the workpiece plane, in addition to data necessary for creating NC data indicative of area cutting, a second step of obtaining the cutting starting point for area cutting by using said data, a third step of calculating coordinate values of said approach starting point using the angle 8 and the distance dz in such a manner that a projection of said straight line on the workpiece plane is brought into orientation with a direction of a normal line at the cutting starting point on the curve of said external shape, and a fourth step of creating NC data for positioning the tool at the approach starting point by using said cutting starting point and the coordinate values of the approach starting point, as well as NC data for moving the tool from the approach starting point to the cutting starting point in a cutting-feed mode, the approach of the tool being controlled based on said NC data.
4. A method of approach in area cutting according to claim 1, characterized in that, in said second step, the normal line is specified by y = a·x + b, and three-dimensional coordinate values (XA, YA, ZA) of an approach starting point are obtained according to
Figure imgb0027
Figure imgb0028
Figure imgb0029
Figure imgb0030
where Pi' is a projection of an approach starting point PA (XA' YA' ZA) on a plane containing a cutting starting point Pi (Xio' Yio' Zio), and D is a distance between Pi and Pi'.
EP84903761A 1983-10-15 1984-10-12 Approaching method in area machining Withdrawn EP0160096A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP58193032A JPS6085812A (en) 1983-10-15 1983-10-15 Approaching method in zone machining
JP193032/83 1983-10-15

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EP (1) EP0160096A1 (en)
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WO (1) WO1985001682A1 (en)

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WO1985001682A1 (en) 1985-04-25
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